Grasping mechanical devices, such as robotic prosthetic devices, for simulating and replacing natural limbs and appendages have been in use for decades. However, the design and operation of such devices generally fail to simulate an appreciable number of the discrete movements of these natural limbs and appendages. For example, hand prosthetic devices range from a passive type, which simulate the appearance of a natural hand but do not move, to newer myoelectric devices, having various combinations of pulleys, cables, linkages and the like with battery-powered operating and control systems, controlled by electromyogram (EMG) signals generated by muscles in a residual limb. In general, these conventional hand prosthetic devices include only a hook or cooperating digits which can grasp an object between them. As a result, they are generally incapable of other grasps or postures. Although, the ability to grasp and hold objects can be a significant improvement for the lifestyle of a hand and/or arm amputee, such amputees are often dissatisfied with the limited utility of such prosthetic devices.